The invention relates to a temperature sensor and, more particularly, to a temperature sensor having a body whose thermal expansion is evaluated in the event of a change in temperature. The magnetic flux in a coil arrangement having at least one coil is modified when the body expands. The change in the magnetic flux in the coil arrangement is evaluated and the change in the magnetic flux is detected as a change in the inductance. The change in length of the body and the change in temperature are deduced therefrom.
A temperature sensor of the above-described type is already known, for example German Patent Document 23 41 998, in which a rod-type expansion sensor, comprising a tubular expansion rod and a reference rod is permanently joined directly to an inductive detector. The reference rod is joined to the armature and the expansion rod to the pot-type cores of the detector which accommodate a coil arrangement. In the event of a change in temperature, the armature, which is joined to the reference rod, alters its position as a result of the thermal expansion of the expansion rod and as a result, the air gap, and consequently the magnetic flux in the coil arrangement, is modified. Independently of its expensive construction, its low response sensitivity is particularly regarded as disadvantageous.
A device is furthermore known for measuring a small path length by the eddy-current principle, for example German Patent Document 27 39 054 A1, in which there is disposed in a coil arrangement, a measuring component which can be acted on by a physical measurable variable as a function of distance. Measuring elements, made of weakly ferromagnetic material, for example of a chrome nickel steel, are in turn disposed on the measuring component in the region of the coil arrangement. The measuring elements act as a short-circuit winding and, depending on the distance of the coil arrangement, are fed with high frequency, and attenuate the coil arrangement to a greater or lesser degree, with the result that the varying impedance is a measure of the measurable variable.
There is therefore needed a temperature sensor of the general type constructed in such a manner that it has as high a response sensitivity as possible and operates at the same time as independently as possible of ambient conditions.
Those needs are met with a temperature sensor according to the present invention, having a body whose thermal expansion is evaluated in the event of a change in temperature. The magnetic flux in a coil arrangement having at least one coil is modified when the body expands. The change in the magnetic flux in the coil arrangement is evaluated and the change in the magnetic flux is detected as a change in the inductance. The change in length of the body and the change in temperature are deduced therefrom. On the body, a layer is deposited by atomic growth. The layer has a layer structure containing less than 8% by weight of phosphorus, preferably up to 3% by weight, up to 2% by weight of an element of main group IV or V, in particular antimony or lead, and up to 5% by weight of a transition metal element, in particular cobalt or iron. The percentages by weight resulting from the sum being increased up to 100% with nickel. The layer also expands with the body and modifies the magnetic flux as a consequence of the change in the permeability of the layer.
According to the present invention, a soft-magnetic layer is applied to a substrate which has as high a thermal coefficient of expansion as possible. The soft magnetic and magnetoelastic layer at the same time modifies the inductance of a coil. As the substrate expands as a result of a change in temperature, the permeability of the layer consequently changes-and, therefore, so does the inductance of the coil. The change in the inductance of the coil can be sensed using means which are known per se.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.